Brushless motor and electric appliance or vehicle equipped with the same

ABSTRACT

The object of the present invention is to provide a low-noise and low-vibration brushless motor and an electric applicance and a vehicle which have the brushless motor and increase in quietness, by optimizing a ratio of the number of poles on a rotor to the number of slots on a stator, the ratio being suitable for a driving circuit. The present invention is a brushless motor constituted by ten-pole rotor ( 1 ), a stator ( 3 ) having (12) slots ( 2 ) and making three-phase connection to the slots ( 2 ), and a driving circuit ( 5 ) for applying three-phase full-wave current to the stator ( 3 ). Further, the conduction width of the driving circuit is set at an electrical angle of 135 to 180°.

TECHNICAL FIELD

[0001] The present invention relates to a brushless motor which isconstituted by a rotor having a plurality of poles, a stator having aplurality of slots and making three-phase connection to the slots, and adriving circuit for applying three-phase full-wave current to thestator, and concerns an electric appliance such as an air conditioner,an air cleaner, and a water heater, or a vehicle that is equipped withthe motor.

BACKGROUND ART

[0002] In recent years, lower noise and lower vibration of brushlessmotors have been in increasing demand. As shown in FIG. 8,conventionally, a brushless motor has been constituted by an eight-polarrotor 1, a stator 3 which has twelve slots 2 and making three-phaseconnection to the slots 2, and a driving circuit 5 which applies 120°three-phase full-wave current to the stator 3. In this way, the ratio ofthe number of poles on the rotor 1 to the number of slots on the stator3 has been 2:3.

[0003] In general, it is said that when current applied to a winding toreduce torque pulsation is brought close to a sine wave, noise andvibration can be effectively reduced. Since voltage applied to a windingis determined by a difference between a line induced voltage and a powersupply voltage, when line induced voltage is closer to a sine wave,noise and vibration can be reduced more effectively.

[0004] However, in the conventional brushless motors, line inducedvoltage has a poor distortion factor, resulting in problems of noise andvibration.

[0005] In FIG. 8, voltage f₈(θ), which is induced by a conductor group12 a on one side of one tooth, is expressed below by Fourier expansion.$\begin{matrix}{{f_{8}(\theta)} = {\sum\limits_{n = 1}^{\infty}{a_{u}\sin \left\{ {\left( {{2n} - 1} \right)\theta} \right\}}}} & \left( {{Equation}\quad 1} \right)\end{matrix}$

[0006] In the above equation, θ represents an electrical angle (°).

[0007] A line induced voltage f₈(θ) is the sum of voltages induced byconductor groups 12 a to 12 p and is obtained by adding 16 phasedifferences of the (equation 1) as shown below.

F ₈(θ)=4f ₈(θ)+8f ₈(θ+60°)+4f ₈(θ+120°)  (Equation 2)

[0008] The equation (2) is expressed for each high-frequency componentas shown below.

F ₈(θ)=12a ₁sin(θ+60°)+12a ₃sin(5θ+300°)+12a ₄sin(7θ+60°)+ . . .  (Equation 3)

[0009] Hence, when the ratio of the number of poles on the rotor to thenumber of slots on the stator is 2:3, although tertiary components ofline induced voltage can be reduced, quintuple and septenary componentscannot be reduced. FIG. 9 shows a line induced voltage waveform at 1000r/min. Since only a sine wave with a distortion factor of 2 to 5% isobtained, torque pulsation occurs, resulting in problems of low noiseand low vibration. Since the 120° three-phase full-wave current-carryingmethod is adopted, when phases of two-phase current application areswitched, current applied to a coil largely fluctuates and torquepulsation occurs, which is a disadvantage against low noise and lowvibration.

DISCLOSURE OF INVENTION

[0010] The present invention in intended to solve the above-mentionedconventional problem, and has an object to provide a low-noise andlow-vibration brushless motor and a more quiet electric appliance and avehicle that are equipped with the brushless motor, by optimizing aratio of the number of poles on a rotor to the number of slots on astator, the ratio being suitable for a driving circuit.

[0011] In order to solve the above-mentioned problem, the presentinvention provides a brushless motor which comprises a rotor having aplurality of poles, a stator having a plurality of slots and makingthree-phase connection to the slots, and a driving circuit for applyingthree-phase full-wave current to the stator, the motor beingcharacterized in that the ratio of the number of poles on the rotor tothe number of slots on the stator is 10:12, and the conduction width ofthe driving circuit is set at an electrical angle of 135 to 180°.

[0012] Further, the brushless motor is mounted in the electric applianceand a vehicle.

BRIEF DESCRIPTION OF DRAWINGS

[0013]FIG. 1 is a diagram showing a sine-wave driving brushless motoraccording to an embodiment of the present invention;

[0014]FIG. 2 is a diagram showing a line induced voltage waveform of thesine-wave driving brushless motor according to the embodiment of thepresent invention;

[0015]FIG. 3 is a structural sectional view showing a sine-wave drivingbrushless motor according to an embodiment of the present invention;

[0016]FIG. 4 is a diagram showing a brushless motor employing a rotor ofa permanent magnet embedded type according to an embodiment of thepresent invention;

[0017]FIG. 5 is a block diagram showing the a structure of an indoorunit and an outdoor unit of an air conditioner according to anembodiment of the present invention;

[0018]FIG. 6a is a block diagram showing a structure of an air cleaneraccording to an embodiment of the present invention;

[0019]FIG. 6b is another block diagram showing the structure of the aircleaner according to the embodiment of the present invention;

[0020]FIG. 7a is a block diagram showing a structure of a water heateraccording to an embodiment of the present invention;

[0021]FIG. 7b is another block diagram showing the structure of thewater heater according to the embodiment of the present invention;

[0022]FIG. 8 is a diagram showing a conventional sine-wave drivingbrushless motor; and

[0023]FIG. 9 is a diagram showing a line induced voltage waveform of theconventional sine-wave driving brushless motor.

DESCRIPTION OF EMBODIMENTS

[0024] In a first invention, a brushless motor comprising a rotor havinga plurality of poles, a stator having a plurality of slots and makingthree-phase connection to the slots, and a driving circuit for applyingthree-phase full-wave current to the stator, characterized in that theratio of the number of poles on the rotor to the number of slots on thestator is 10:12 and the conduction width of the driving circuit is setat an electrical angle of 135 to 180°. Thus, it is possible to reducequintuple and septenary components as well as a tertiary component ofline induced voltage and to bring line induced voltage to a sine wave,thereby obtaining low noise and low vibration. Further, since theconduction width of the driving circuit is set at an electrical angle of135 to 180°, it is possible to reduce fluctuations in current applied toa coil because a three-phase conducting period is provided when phasesare switched, and it is possible to reduce torque pulsation, therebyobtaining low noise and low vibration.

[0025] In a second invention, a brushless motor comprising a rotorhaving a plurality of poles, a stator having a plurality of slots andmaking three-phase connection to the slots, and a driving circuit forapplying three-phase full-wave current to the stator, characterized inthat the ratio of the number of poles on the rotor to the number ofslots on the stator is 10:12 and the driving circuit is a sine-wavedriving circuit. In the sine-wave driving circuit, the following drivingcircuit method is used: voltage applied to a winding is subjected to PWMcontrol according to a difference between a line induced voltage and apower supply voltage, and current applied to the winding is broughtclose to a sine wave. Thus, current applied to a coil can be broughtclose to a sine wave. Moreover, since the ratio of the number of poleson the rotor to the number of slots on the stator is 10:12, line inducedvoltage can be brought close to a sine wave and torque pulsation can bereduced, thereby obtaining low noise and low vibration.

[0026] In a third invention, a brushless motor comprising a rotor havinga plurality of poles, a stator having a plurality of slots and makingthree-phase connection to the slots, and a driving circuit for applyingthree-phase full-wave current to the stator, characterized in that theratio of the number of poles on the rotor to the number of slots on thestator is 10:12 and the conduction width of the driving circuit is setat an electrical angle of 150°. Hence, it is possible to bring lineinduced voltage close to a sine wave and to bring current applied to awinding close to a sine wave, thereby obtaining low noise and lowvibration.

[0027] A fourth invention is the brushless motor of the third invention,characterized in that the conduction width of the driving circuit is setat an electrical angle of 150°, current applied to phase coils isexpressed as a first value during an overlapping period when adjacentphase coils of the phase coils enter the same current-carrying state,and the current is expressed as a second value in a period other thanthe overlapping period. Thus, current applied to a winding can be closerto a sine wave as compared with the third invention, thereby obtaininglow noise and low vibration.

[0028] A fifth invention is the brushless motor of the fourth inventioncharacterized in that the ratio of the first value and the second valueis sin (π/3):1 (approximately 0.866:1). It is possible to reduce noiseand vibration most effectively at 150° current application.

[0029] A sixth invention is the brushless motor according to any one ofthe first to fifth inventions, the brushless motor comprising a rotorhaving a plurality of poles, a stator having a plurality of slots andmaking three-phase connection to the slots, and a driving circuit forapplying three-phase full-wave current to the stator, characterized inthat the ratio of the number of poles on the rotor to the number ofslots on the stator is 10:12, the conduction width of the drivingcircuit is set at an electrical angle of 135 to 180°, and the drivingcircuit is mounted in the motor. Thus, it is possible to obtain lownoise, low vibration, and a small size.

[0030] A seventh invention is the brushless motor according to any oneof the first to sixth inventions, characterized in that the rotor has astructure of a permanent magnet embedded type. Thus, the ratio of thenumber of poles on the rotor to the number of slots on the stator is10:12 while a quantity of magnetic flux is increased on the magnet, sothat line induced voltage can be brought close to a sine wave andcurrent applied to a winding can be brought close to a sine wave,thereby obtaining high efficiency in addition to low noise and lowvibration.

[0031] An eighth invention is an electric appliance equipped with thebrushless motor according to any one of the first to seventh inventions,the electric appliance being characterized by reducing resonance withthe main body of the electric appliance during an operation of thebrushless motor.

[0032] A ninth invention is a vehicle equipped with the brushless motoraccording to any one of the first to seventh inventions, the vehiclebeing characterized by reducing resonance with the main body of thevehicle during an operation of the brushless motor. It is possible toobtain low noise and low vibration during the operation.

[0033] The following will discuss embodiments of the present inventionin accordance with the drawings.

[0034] (Embodiment 1)

[0035]FIG. 1 shows a brushless motor which comprises a ten-pole rotor 1having north pole permanent magnets and south pole permanent magnetsalternately disposed, a stator 3 having 12 slots 2 and makingthree-phase connection to the slots 2, and a driving circuit 5 forapplying three-phase full-wave current to the stator 3. Stator windingsof a U phase, a V phase, and a W phase are wound around the stator. Eachof the phases is composed of four windings, and the windings in a pairare opposed to each other.

[0036] Voltage f₁₀(θ), which is induced by a conductor group 12 a on oneside of one tooth, is expressed below by Fourier expansion.$\begin{matrix}{{f_{10}(\theta)} = {\sum\limits_{n = 1}^{\infty}{b_{n}\sin \left\{ {\left( {{2n} - 1} \right)\theta} \right\}}}} & \left( {{Equation}\quad 4} \right)\end{matrix}$

[0037] In the above equation, θ represents an electrical angle (°).

[0038] A line induced voltage f₁₀(θ) is the sum of voltages induced byconductor groups 12 a to 12 p and is obtained by adding 16 phasedifferences of the (equation 4) as shown below.

F ₁₀(θ)=2f ₁₀(θ)+4f ₁₀(θ+30°)+4f ₁₀(θ+60°)+4f ₁₀(θ+90°)+2f₁₀(θ+120°)  (Equation 5)

[0039] The equation (5) is expressed for each high-frequency componentas shown below.

F ₁₀(θ)=12.93b ₁sin(θ+60°)+0.93b ₃sin(5θ+120°)+0.93b ₄sin(7 θ+240°)+ . .. (Equation 6)

[0040] In this way, in the case of the brushless motor in which theratio of the number of poles on the rotor to the number of slots on thestator is 10:12, it is possible to reduce quintuple and septenarycomponents as well as a tertiary component of line induced voltage. FIG.2 shows a line induced voltage waveform at 1000 r/min. It is possible toobtain a sine wave with a distortion factor decreasing to 0.7% so as toreduce torque pulsation, thereby obtaining low noise and low vibration.

[0041] Further, the conduction width of the driving circuit is set at anelectrical angle of 135 to 180°. Thus, a three-phase conducting periodis provided when phases are switched, so that it is possible to reducefluctuations in current applied to a coil so as to reduce torquepulsation, thereby obtaining low noise and low vibration.

[0042] Furthermore, the driving circuit is formed as a sine-wave drivingcircuit. Thus, current applied to the coil is brought close to a sinewave, so that noise and vibration can be further reduced.

[0043] Besides, the conduction width of the driving circuit 5 is set atan electrical angle of 150°. Hence, it is possible to bring line inducedvoltage close to a sine wave and to bring current applied to a windingclose to a sine wave, thereby obtaining low noise and low vibration.

[0044] Additionally, current applied to phase coils is expressed as afirst value during an overlapping period when adjacent phase coils ofthe phase coils enter the same current-carrying state, and the currentis expressed as a second value in a period other than the overlappingperiod. Thus, current applied to a winding can be brought closer to asine wave as compared with the third invention, thereby obtaining lownoise and low vibration.

[0045] Further, the ratio of the first value and the second value is sin(π/3):1 (approximately 0.866:1). It is possible to reduce noise andvibration most effectively at 150° current application.

[0046] (Embodiment 2)

[0047]FIG. 3 is a structural sectional view showing a sine-wave drivingbrushless motor according to an embodiment of the present invention.Reference numeral 1 denotes a rotor, reference numeral 3 denotes astator making three-phase connection to slots, reference numeral 4denotes a winding, reference numeral 5 denotes a driving circuit forapplying three-phase full-wave current to the stator 3, referencenumeral 6 denotes a bearer, reference numeral 7 denotes rubber vibrationisolators, reference numeral 8 denotes mold resin, reference numeral 9denotes a shaft, reference numeral 10 denotes a bracket, and referencenumeral 11 denotes a rotor core. In the present embodiment, thesine-wave driving circuit 5 is mounted in the motor. The size can bereduced by integrating the motor and the circuit.

[0048] (Embodiment 3)

[0049]FIG. 4 shows a brushless motor which comprises a ten-pole rotor 1having a permanent magnet embedded rotor structure, in which north poleand south pole magnets 50 are alternately disposed on a rotor core 11, astator 3 having 12 slots 2 and making three-phase connection to theslots 2, and a driving circuit 5 for applying three-phase full-wavecurrent to the stator 3. Since the rotor structure is the permanentmagnet embedded type, the ratio of the number of poles on the rotor tothe number of slots on the stator is 10:12 while a quantity of magneticflux is increased on the magnet, so that it is possible to bring lineinduced voltage close to a sine wave and to bring current applied to awinding to a sine wave, thereby obtaining high efficiency in addition tolow noise and low vibration.

[0050] (Embodiment 4)

[0051] An indoor unit 13 and an outdoor unit 14 in an air conditioner ofFIG. 5 are equipped with motors of the fourth invention. In the indoorunit 13, a cross flow fan 17 is mounted on a motor 26 for blowing. Inthe outdoor unit 14, a propeller fan 18 is mounted on a motor 27 forblowing air onto a heat exchanger 16. These fan motors are also operatedwhen the air conditioner is operated. Besides, in FIG. 5, referencenumeral 15 denotes a heat exchanger for the internal device, referencenumeral 16 denotes a heat exchanger for the external device, referencenumerals 19 and 20 denote controllers, reference numeral 21 denotes acompressor, reference numeral 22 denotes a power supply line, referencenumeral 23 denotes a signal line, reference numeral 24 denotes arefrigerant pipe, and reference numeral 25 denotes a power supply inputline.

[0052] In this way, when the present invention is used for a fan motorof an air conditioner, it is possible to reduce resonance on the fansand main bodies of the units during an operation of the air conditioner,thereby obtaining low noise and low vibration.

[0053] (Embodiment 5)

[0054] A water heater 28 of FIG. 6a is equipped with a motor of thefourth invention as a blowing fan motor 38 for supplying air requiredfor burning. A multiblade fan 40 of FIG. 6b is mounted on the blowingfan motor 38. Besides, in FIG. 6a, reference numeral 30 denotes a hotwater pipe, reference numeral 31 denotes a water pipe, reference numeral32 denotes a burner, reference numeral 33 denotes a control section,reference numeral 34 denotes a fuel pump, reference numeral 35 denotes acarburetor, reference numeral 36 denotes a fuel pipe, and referencenumeral 37 denotes a fuel tank. In FIG. 6b, reference numeral 39 denotesa casing, and reference numeral 41 denotes an exhaust port.

[0055] In Embodiment 5 as well, it is possible to reduce resonance ofthe fan and the main body of the appliance during an operation of thewater heater, thereby obtaining low noise and low vibration.

[0056] (Embodiment 6)

[0057] Further, an air cleaner 42 of FIGS. 7a and 7 b is equipped with amotor of the fourth invention as a blowing motor. A multiblade fan 40 ismounted on a blowing motor 49 of the air cleaner. In FIGS. 7a and 7 b,reference numeral 43 denotes a control plate, reference numeral 44denotes an air filter, reference numeral 45 denotes an exhaust port,reference numeral 46 denotes an inlet port, and reference numeral 47denotes an operating plate. In Embodiment 6 as well, it is possible toreduce resonance of the fan and the main body of the appliance during anoperation of the air cleaner, thereby obtaining low noise and lowvibration.

[0058] Additionally, the present invention is not limited to the aboveembodiments. In other uses, the present invention can be mounted as afan motor of an air conditioner for a vehicle where quietness: in a roomis demanded, a fan motor for cooling a radiator, and a motor for drivingan electric bicycle.

[0059] As described above, according to the first invention, lineinduced voltage can be closer to a sine wave as compared with abrushless motor in which the ratio of the number of poles on a rotor tothe number of slots on a stator is 2:3. Further, the conduction width ofthe driving circuit is set at an electrical angle of 135 to 180°, sothat it is possible to reduce fluctuations in current applied to a coilbecause a three-phase conducting period is provided when phases areswitched, and torque pulsation is reduced, thereby obtaining low noiseand low vibration.

[0060] Moreover, according to the second invention, the driving circuitis formed as a sine-wave driving circuit. Hence, the following drivingcircuit method is used: voltage applied to a winding is subjected to PWMcontrol according to a difference between a line induced voltage and apower supply voltage, and current applied to the winding is broughtclose to a sine wave. Thus, current applied to a coil can be broughtclose to a sine wave. Moreover, since the ratio of the number of poleson the rotor to the number of slots on the stator is set at 10:12, lineinduced voltage can be brought close to a sine wave and torque pulsationcan be reduced, thereby obtaining low noise and low vibration.

[0061] Besides, according to the third invention, the conduction widthof the driving circuit is set at an electrical angle of 150°. Hence,line induced voltage can be brought close to a sine wave and currentapplied to a winding can be brought close to a sine wave, therebyobtaining low noise and low vibration.

[0062] Also, according to the fourth invention, the conduction width ofthe driving circuit is set at an electrical angle of 150°, power appliedto phase coils is expressed as a first value during an overlappingperiod when adjacent phase coils of the phase coils enter the samecurrent-carrying state, and the power is expressed as a second value ina period other than the overlapping period. Thus, current applied to awinding can be closer to a sine wave, thereby achieving a brushlessmotor with lower noise and lower vibration.

[0063] In addition, according to the fifth invention, the ratio of thefirst value and the second value is sin (π/3):1 (approximately 0.866:1).It is possible to obtain a brushless motor which has the lowest noiseand vibration at 150° current application.

[0064] Further, according to the sixth invention, the ratio of thenumber of poles on the rotor to the number of slots on the stator is10:12, a conduction width of the driving circuit is set at an electricalangle of 135 to 180°, and the driving circuit is mounted in the motor.Thus, it is possible to obtain a brushless motor which can bring lineinduced voltage to a sine wave, reduce fluctuations in current appliedto the coil by the driving circuit, and reduce torque pulsation with lownoise, low vibration, and a small size.

[0065] Moreover, according to the seventh invention, since the rotor hasthe permanent magnet embedded structure, the ratio of the number ofpoles on the rotor to the number of slots on the stator is 10:12 while aquantity of magnetic flux is increased on the magnet, so that lineinduced voltage can be brought close to a sine wave and current appliedto a winding can be brought close to a sine wave. Besides, theconduction width of the driving circuit is set at an electrical angle of135 to 180°, so that it is possible to reduce fluctuations in currentapplied to the coil, thereby obtaining high efficiency in addition tolow noise and low vibration.

[0066] In general, when the rotor has the permanent magnet embeddedstructure, a magnetic flux between poles is larger than that of a rotorwith a surface magnetic structure in a gap magnetic flux distributionbetween the rotor and the stator. Thus, line induced voltage has a poordistortion factor. Hence, in a conventional brushless motor in which theratio of the number of poles on the rotor to the number of the slots onthe stator is 2:3, line induced voltage has a poor distortion factor.The brushless motor is more efficient than a rotor with a surface magnetstructure but is larger in noise and vibration. However, since the ratioof the number of poles on the rotor to the number of slots on the statoris 10:12, it is possible to reduce quintuple and septenary components aswell as a tertiary component of line induced voltage and to bring lineinduced voltage to a sine wave, thereby obtaining low noise and lowvibration.

[0067] Furthermore, according to the eighth and ninth inventions, it ispossible to reduce resonance on the main body of an electric applianceor the main body of a vehicle, thereby reducing low noise and lowvibration.

1. A brushless motor, comprising a rotor having a plurality of poles, astator having a plurality of slots and making three-phase connection tothe slots, and a driving circuit for applying three-phase full-wavecurrent to the stator, characterized in that a ratio of the number ofpoles on the rotor to the number of slots on the stator is 10:12 and aconduction width of the driving circuit is set at an electrical angle of135 to 180°.
 2. The brushless motor according to claim 1, characterizedin that a ratio of the number of poles on the rotor to the number ofslots on the stator is 10:12 and the driving circuit is a sine-wavedriving circuit.
 3. The brushless motor according to claim 1,characterized in that a ratio of the number of poles on the rotor to thenumber of slots on the stator is 10:12 and a conduction width of thedriving circuit is set at an electrical angle of 150°.
 4. The brushlessmotor according to claim 3, characterized in that a conduction width ofthe driving circuit is set at an electrical angle of 150°, currentapplied to phase coils is expressed as a first value during anoverlapping period when adjacent phase coils of the phase coils enterthe same current-carrying state, and the current is expressed as asecond value in a period other than the overlapping period.
 5. Thebrushless motor according to claim 4, characterized in that a ratio ofthe first value and the second value is sin (π/3):1 (approximately0.866:1).
 6. The brushless motor according to any one of claims 1 to 5,characterized in that a ratio of the number of poles on the rotor to thenumber of slots on the stator is 10:12, a conduction width of thedriving circuit is set at an electrical angle of 135 to 180°, and thedriving circuit is mounted in the motor.
 7. The brushless motoraccording to any one of claims 1 to 6, characterized in that the rotorhas a structure of a permanent magnet embedded type.
 8. An electricappliance, comprising the brushless motor according to any one of claims1 to
 7. 9. A vehicle, comprising the brushless motor according to anyone of claims 1 to 7.